Question

我遇到一段代码要弹出到导航堆栈中的特定viewcontroller，如下所示

for (UIViewController* viewController in self.navigationController.viewControllers) {
    if ([viewController isKindOfClass:[MyGroupViewController class]] ) {
        MyGroupViewController *groupViewController = (MyGroupViewController*)viewController;
        [self.navigationController popToViewController:groupViewController animated:YES];
    }
}

目标是弹出MyGroupViewController。但我不理解这行代码。

MyGroupViewController *groupViewController = (MyGroupViewController*)viewController;

这里到底发生了什么。我不认为在这里创建了一个新的MyGroupViewController实例。

Answer 1

//This for loop iterates through all the view controllers in navigation stack.   
for (UIViewController* viewController in self.navigationController.viewControllers) {

    //This if condition checks whether the viewController's class is MyGroupViewController 
    // if true that means its the MyGroupViewController (which has been pushed at some point)
    if ([viewController isKindOfClass:[MyGroupViewController class]] ) {

        // Here viewController is a reference of UIViewController base class of MyGroupViewController 
        // but viewController holds MyGroupViewController  object so we can type cast it here
        MyGroupViewController *groupViewController = (MyGroupViewController*)viewController;
        [self.navigationController popToViewController:groupViewController animated:YES];
    }
}

你也可以这样做

if ([viewController isKindOfClass:[MyGroupViewController class]] ) {
            [self.navigationController popToViewController:viewController  animated:YES];
 }

Swift代码

//Itrate through all the view controllers in navigation stack
for vc in self.navigationController!.viewControllers {
  // Check if the view controller is of MyGroupViewController type
  if let myGropupVC = vc as? MyGroupViewController {
    self.navigationController?.popToViewController(myGropupVC, animated: true)
  }
}

Answer 2

正在枚举导航控制器堆栈的视图控制器。由于这些视图控制器可以是任何类型（但始终从UIViewController继承），因此使用通用的UIViewController。但是，编译器将不知道该视图控制器是什么类型，因此它被转换为MyGroupViewController。当发生这种情况时，编译器会知道类的类型，并且可以向它发送仅适用于该类的消息。

在这种情况下，它有点不必要，因为它可以简化为：

(UIViewController* viewController in self.navigationController.viewControllers) {
    if ([viewController isKindOfClass:[MyGroupViewController class]] ) {
        [self.navigationController popToViewController:viewController animated:YES];
    }
}

简答：它将变量类型更改为括号中指定的类型，以避免编译器警告。

Answer 3

for (int m=0; m<[self.navigationController.viewControllers count]; m++)   
{  

        if([[self.navigationController.viewControllers objectAtIndex:m] isKindOfClass:[MyGroupViewController class]])  
            { 

                MyGroupViewController * groupViewController = [self.navigationController.viewControllers    objectAtIndex:m];  
                [self.navigationController popToViewController:groupViewController animated:YES];   
             }   
}

Answer 4

- (void) RetunToSpecificViewController{

    for (UIViewController *controller in self.navigationController.viewControllers) {
        if ([controller isKindOfClass:[AnOldViewController class]]) { 
        //Do not forget to import AnOldViewController.h

            [self.navigationController popToViewController:controller
                                              animated:YES];
            break;
        }
    }

On Swift

func RetunToSpecificViewController()
{
    let viewControllers: [UIViewController] =  self.navigationController!.viewControllers as [UIViewController]
  self.navigationController!.popToViewController(viewControllers[viewControllers.count
        - 5], animated: true)
}

我们已经写了一篇更好的教程，你可以检查一下 https://appengineer.in/2014/03/13/pop-to-specific-view-controller-in-ios/

弹出到导航堆栈中的特定viewcontroller

4 个答案: